A rock cycle shows how one rock can turn into a different rock and the process it must undergo in order to become that rock. It shows every possibility a rock can take in order to become a different rock.
Any rock can turn into all thre types of rocks. For instance, a sedimentary rock can melt and turn into an igneous rock or go through heat and pressure and turn into a metamorphic rock. It can also break down again and then compact itself together to a reformed sedimentary rock